Scanning method and apparatus

ABSTRACT

A scanning apparatus and method, the apparatus comprising: a light transmission means ( 90 ) having an exit tip; first and second drive means ( 92,94 ) for resonantly driving the light transmission means ( 90 ) in orthogonal directions; wherein the first and second drive means ( 92,94 ) are operable to move the tip in an elliptical pattern while varying the eccentricity of the elliptical pattern, whereby a portion of the elliptical pattern having a centre on the minor axis of the elliptical pattern approximates—at least in appearance—a raster pattern.

FIELD OF THE INVENTION

The present invention relates to a scanning method and apparatus, ofparticular but by no means exclusive application in scanning fibremicroscope and scanning fibre endoscopes.

BACKGROUND OF THE INVENTION

One existing scanning technique employs a resonant cantilever in orderto achieve the high frequency scanning of an optical fibre tip, as acompact alternative to resonant mirror/galvanometer scanners. The highfrequency or X scan is then combined with a slow or Y scan to produce astandard raster scanning pattern. The slow scan is usually not resonantand can have a sawtooth function, with relatively rapid retrace.

In such an arrangement, mechanical considerations require a resonantsinusoidal spot motion in the X or fast direction of the scan. Althougha TV raster in both directions is more desirable (for optical dosagecontrol and data gathering), a sawtooth scan at constant speed isfeasible in only the slow or Y direction. As shown in FIG. 12, underpractical conditions about half the scan area is available for dataacquisition as indicated by the solid curves for a typical square imagearea. It is a matter of simple geometry to calculate that, at the end ofthe solid curves, the spot speed has fallen to 87% of the peak spotspeed. The dotted portion of the scan, where spot speed is less than 87%of this maximum, is discarded. The 87% figure is derived from the 87%value for the maximum derivative of the cosine value. This value issomewhat arbitrary, but provides a basis for comparison betweendifferent scan patterns. The choice of 87% originates from theinventors' use of half of the amplitude of the sine wave for the rasterscan, which corresponds to the ≧87% of maximum speed section of theraster pattern. This is also regarded, based on the inventors'experience, as the acceptable region in terms of image quality withoutundue distortion.

Typically in existing systems, the Y mechanism is in tandem with the Xdeflection system and has similar length. However, as demand increasesfor ever more compact scanners there is a need to develop a combined XYscanner of shortest possible length. If the fibre can itself bedeflected in both X and Y directions, as a symmetrical cantilever, thescanner is more compact. The problem is that for practical forces onlyresonant operation is feasible. For this reason modulated circularpatterns have been developed, such as is disclosed in U.S. Pat. No.6,294,775 (Seibel and Furness).

U.S. Pat. No. 6,294,775 discloses a system in which a fibre tip istypically moved in a circle or ellipse, the radius of which is thenmodulated so that an area is progressively scanned. Suitably phased Xand Y drives can produce the circular motion, effectively resonant inboth X and Y directions. However, the modulation of the radius of thescanning circle or ellipse results in a large variation in scanningspeed, and a singularity at the centre of the field. This scan patternis very different from a raster scan, so the resulting circular patternrequires image processing, creating interface problems with standardsystems. One pattern that can be produced with the system of U.S. Pat.No. 6,294,775 is shown schematically in FIG. 13. Only that portion ofthe scan shown with a solid curve would be used for imaging. The portionof the scan shown with a dotted curve corresponds to a spot speed ofless than 87% of the peak scan speed and is discarded. Hence most of thecentral area cannot be accessed. The solid curve again corresponds to aspot speed of ≧87% of the peak spot speed which, in this spiral scan,corresponds to a radius of 87% of the maximum radius.

SUMMARY OF THE INVENTION

In a first broad aspect the present invention provides, therefore, amethod of scanning a light transmission means having an exit tip,comprising moving said tip in an elliptical pattern while varying theeccentricity of said elliptical pattern.

Thus, one portion of the elliptical pattern (centred on the minor axisof the elliptical pattern) approximates—at least in appearance—a rasterpattern.

Preferably the eccentricity is varied by varying the length of one axisof said elliptical pattern. More preferably the eccentricity is variedby varying the length of the minor axis of said elliptical pattern

The central portion of an ellipse (either to one side of the major axisor spanning the major axis) approximates a rectangle, especially whenthat portion is narrow in the direction of the major axis, so—as theeccentricity of the elliptical pattern is varied—a scan pattern willresult that approximates in appearance a raster pattern. Some barreldistortion will result, but this form of distortion can be tolerableor—if not—is relatively easily corrected by image processing. In anyevent, relative to the prior art modulation of radius technique, thisdistortion is small. The ellipse could even be a circle at its point ofminimum eccentricity (that is, an ellipse with an eccentricity of zero),if—in certain applications—the resulting distortion were tolerable orcorrectable.

It should also be understood that the term light is used above toinclude all forms of electromagnetic radiation. Preferably theeccentricity is repeatedly varied between a minimum value and one. Morepreferably the eccentricity is repeatedly varied from a minimum value toone and then back to said minimum value, and said portion is centred onthe centre of said elliptical pattern.

Preferably said elliptical pattern has a major axis and minor axis inthe ratio of approximately two.

Preferably said method includes modulating said eccentricity bymodulating the minor axis of said elliptical pattern between positiveand negative extremes, so that said tip moves in both clockwise andcounterclockwise directions in the course of a single complete scan.

Preferably said method includes driving said tip with an X driveparallel to the major axis of said elliptical pattern and with a Y driveparallel to the minor axis of said elliptical pattern, and synchronisingat a constant phase to the X scan to allow interfacing to a standardraster display.

Preferably said Y drive is derived by synchronously switching a delayedversion of said X drive.

For example, drive signals can be square waves, so any phase shiftingcan be accomplished by simple delay circuits.

Preferably said light transmission means is an optical fibre.

Preferably the method includes driving said light transmission meansmagnetically. More preferably the method includes driving said lighttransmission means by means of a magnet attached to said lighttransmission means, wherein said magnet is magnetised axially and actedon by mutually perpendicular coils or windings.

More preferably, said mutually perpendicular coils or windings comprisea pair of drive coils located symmetrically each on opposite sides of arest position of said magnet in a first plane, and a further drive coillocated in a second plane perpendicular to said first plane; and themethod further comprises:

-   -   sensing the position of said magnet by means of a sensing coil        located in said second plane symmetrically opposite said magnet        from said further drive coil;    -   obtaining an output signal from said sensing coil indicative of        said position of said magnet; and    -   deriving an input signal for said further drive coil from said        output signal;    -   wherein each of said pair of drive coils, said further drive        coil, and said sensing coil are equidistant from said magnet in        said rest position.

Preferably said method includes controlling a) said pair of coils insaid first plane and b) said further coil and said sensing coil in saidsecond plane, to swap functions so that said pair of drive coils in saidfirst plane act as a drive coil and a sensing coil, and said furthercoil and said sensing coil in said second plane act as a pair of drivecoils, whereby a further scan can be performed perpendicular to saidelliptical pattern.

In one embodiment, the light transmission means is provided with a coatof magnetic material. Alternatively, the light transmission means islocated within a close-fitting magnetic tube.

These options permit the resonant frequency and length to be matched todesign requirements.

In a second broad aspect, the present invention provides a scanningapparatus, comprising:

-   -   a light transmission means having an exit tip;    -   first and second drive means for resonantly driving said light        transmission means in orthogonal directions;    -   wherein said first and second drive means are operable to move        said tip in an elliptical pattern while varying the eccentricity        of said elliptical pattern.

Preferably the apparatus is operable to vary said eccentricity byvarying the length of one axis of said elliptical pattern. Morepreferably apparatus is operable to vary said eccentricity by varyingthe length of the minor axis of said elliptical pattern

Preferably the apparatus is operable to repeatedly vary saideccentricity between a minimum value and one. More preferably theapparatus is operable to repeatedly said eccentricity from a minimumvalue to one and then back to said minimum value, wherein said portionis centred on the centre of said elliptical pattern.

Preferably said elliptical pattern has a major axis and minor axis inthe ratio of approximately two.

Preferably said apparatus is operable to modulate said eccentricity bymodulating the minor axis of said elliptical pattern between positiveand negative extremes, so that said tip moves in both clockwise andcounterclockwise directions in the course of a single complete scan.

Preferably the apparatus is operable to drive said tip with an X driveparallel to the major axis of said elliptical pattern and with a Y driveparallel to the minor axis of said elliptical pattern, and tosynchronise at a constant phase to the X scan to allow interfacing to astandard raster display.

Preferably said Y drive is derived by synchronously switching a delayedversion of said X drive.

Preferably said light transmission means is an optical fibre.

Preferably the apparatus includes a magnetic drive for driving saidlight transmission means. More preferably said magnetic drive includes amagnet attached to said light transmission means and mutuallyperpendicular coils or windings, wherein said magnet is magnetisedaxially and acted on by said mutually perpendicular coils or windings.

More preferably, said mutually perpendicular coils or windings comprisea pair of drive coils located symmetrically each on opposite sides of arest position of said magnet in a first plane, and a further drive coillocated in a second plane perpendicular to said first plane, and saidapparatus further comprises a sensing coil for sensing the position ofsaid magnet and located in said second plane symmetrically opposite saidmagnet from said further drive coil, wherein each of said pair of coils,said further coil and said sensing coil are equidistant from said magnetin said rest position, said sensing coil is operable to output an outputsignal indicative of said position of said magnet, and said apparatus isoperable to derive an input signal for said further coil from saidoutput signal.

Preferably said apparatus is operable to control a) said pair of coilsin said first plane and b) said further coil and said sensing coil insaid second plane, to swap functions so that said pair of drive coils insaid first plane act as a drive coil and a sensing coil, and saidfurther coil and said sensing coil in said second plane act as a pair ofdrive coils, wherein said apparatus can perform a further scanperpendicular to said elliptical pattern.

The magnet can be in any suitable form. Hence, in one embodiment, thelight transmission means is provided with a magnet in the form of a coatof magnetic material. Alternatively, the light transmission means islocated within a magnet in the form of a close-fitting magnetic tube.

In a third broad aspect, the invention provides a scanning apparatuscomprising:

-   -   an X drive for driving a light transmission means having an exit        tip in an X direction;    -   a Y drive for driving a light transmission means having an exit        tip in a Y direction;    -   an X drive input signal generator for providing an X drive input        signal; and    -   a Y drive input signal generator for providing a Y drive input        signal modulated by a modulating signal derived from said X        drive input signal;    -   wherein said exit tip executes a scan pattern when driven        simultaneously by said X drive and said Y drive.

Thus, with this scanning apparatus resonant and non-resonant scanpatterns can be generated, including spiral patterns, figure eight scanpatterns, and elliptical (including circular) scan patterns.

In a fourth broad aspect, the invention provides a scanning apparatuscomprising:

-   -   an X drive for driving a light transmission means having an exit        tip in an X direction;    -   a Y drive for driving a light transmission means having an exit        tip in a Y direction;    -   an X drive input signal generator for providing a square wave X        drive input signal; and    -   a Y drive input signal generator for providing a Y drive input        signal by generating a sawtooth signal and modulating said        sawtooth signal with a modulating signal derived from said X        drive input signal;    -   wherein said exit tip executes a scan pattern when driven        simultaneously by said X drive and said Y drive.

The following features are preferred in both the third and fourth broadaspects.

Preferably the scan pattern is elliptical and has an eccentricity thatis always greater than zero (that is, the scan pattern has anon-circular envelope).

Preferably said Y drive input signal generator is operable to generatesaid sawtooth signal such that said sawtooth signal is repeatedlyinverted according to a trigger signal comprising a delayed version ofsaid X drive input signal.

Preferably said apparatus is operable to collect image data from acentral portion of said scan pattern. More preferably said apparatus isoperable to collect image data from a central portion of said scanpattern corresponding to an exit tip speed of greater than or equal toapproximately 87% of a peak exit tip speed.

The invention also provides an optical fibre endoscope, microscope orendomicroscope comprising a scanning apparatus as described above.

BRIEF DESCRIPTION OF THE DRAWING

In order that the present invention may be more clearly ascertained,preferred embodiments will now be described, by way of example, withreference to the accompanying drawing, in which:

FIG. 1A is a schematic diagram of the start of an elliptical scanaccording to a first preferred embodiment of the present invention inwhich the scan commences clockwise;

FIG. 1B is a schematic diagram of the scan of FIG. 1A just past itsmid-point and now proceeding anti-clockwise;

FIG. 1C is a schematic diagram of the data acquisition portion of onecomplete cycle of the scan of FIG. 1A;

FIG. 2 is a schematic diagram of the Y drive signal used to produce thescan of FIG. 1A;

FIG. 3 is a schematic diagram of the Y drive signal used to produce ascan according to a second preferred embodiment of the invention;

FIG. 4 is a schematic diagram of the Y drive signal used to produce ascan according to a third preferred embodiment of the invention;

FIG. 5 is a schematic circuit diagram of a scanning apparatus of afourth preferred embodiment of the present invention;

FIG. 6 is a diagram of the coil driving mechanisms of the apparatus ofFIG. 5;

FIG. 7 is a schematic diagram of a scanning apparatus, includingassociated electronics, according to a fifth preferred embodiment of thepresent invention;

FIG. 8A is a schematic diagram of a sawtooth Y signal provided by theimaging electronics of the apparatus of FIG. 7;

FIG. 8B is a schematic diagram of an X sensing signal that is a functionof the position of the magnet of the apparatus of FIG. 7;

FIG. 8C is a schematic diagram of the X drive input signal of theapparatus of FIG. 7;

FIG. 8D is a schematic diagram of a switch control signal of theapparatus of FIG. 7;

FIG. 8E is a schematic diagram of the Y drive input signal of theapparatus of FIG. 7;

FIG. 9A is a partial cross-sectional view of an endoscope head providedwith the apparatus of FIG. 7;

FIG. 9B is an end view of an optional collar for the optical fibre ofthe apparatus of FIG. 7;

FIG. 9C is a partial cross-sectional view of an endoscope head providedwith a variation of the apparatus of FIG. 7;

FIG. 10A depicts plots of resonant frequency against fibre length forthe apparatus of FIG. 7, without a magnet, with a magnet of 2 mm lengthand 0.40 mm diameter, and with a magnet of 2 mm length and 0.48 mmdiameter;

FIG. 10B depicts plots of radius of tip movement against fibre lengthfor the apparatus of FIG. 7, for a magnet of 2 mm length and 0.48 mmdiameter and of 2 mm length and 0.40 mm diameter;

FIG. 10C depicts plots of mechanical magnification (calculated as theratio of fibre tip deflection to magnet deflection) against fibrelength, for a magnet of 2 mm length and 0.48 mm diameter and of 2 mmlength and 0.40 mm diameter;

FIG. 11 depicts the results of a theoretical comparison of scan areasobtained for raster patterns obtained with a prior art tuning-fork typescanning mechanism and with an apparatus comparable to that of FIG. 7;

FIG. 12 is a schematic diagram of a prior art resonant X, sawtooth Yscan in which solid curves indicate the imaged scan area and dashedcurves the discarded scan area; and

FIG. 13 is a schematic diagram of a prior art resonant X, sawtooth Yscan in which the solid curve indicates the imaged scan area and thedashed curve the discarded scan area.

DETAILED DESCRIPTION

An elliptical scan pattern according to a first preferred embodiment ofthe present invention is shown, soon after commencement, at 10 in FIG.1A. In this figure (and in FIGS. 1B and 1C), a broken curve indicatesthose portions of this scan where no data acquisition is occurring; asolid curve indicates data acquisition.

The scan traces out a first ellipse 12 with a major axis twice thelength of its minor axis (that is, with an eccentricity of approximately0.87).

When the scan reaches the top, central region of ellipse 12 (that is, atpoint 14 to the left of the minor axis) data acquisition is triggeredand continues to a comparable point 16 to the right of the centre of theellipse 12 at which data acquisition is stopped. Thus, data is acquiredover an arc with a length approximately equal to the semi-major axis ofthe ellipse 12. Although this arc has some curvature, this does not leadto an excessive level of distortion if processed as though it werestraight. In addition, it is possible by conventional means to processany image collected by this technique to remove that distortion(producing thereby an image with curved upper and lower sides).

The first ellipse 12 is completed when its lower, fly-back section istraced. During non-data acquisition portions generally, either a lightsignal can be received but be discarded, or the source of light can beswitched off or obscured so that in fact no data is generated.

The scan then proceeds, but with a lower Y drive signal so that the nextellipse (whose initial portion 18 is indicated in the figure) has thesame major axis as the first ellipse 12, but a smaller minor axis andhence greater eccentricity. Data is acquired between points 20 and 22,which are aligned vertically with, respectively, points 14 and 16 offirst ellipse 12. The resulting data acquisition trace 24 isconsequently displaced downwards relative to the first data acquisitiontrace 26, and has a smaller curvature.

The scan proceeds in this manner, with progressively decreasing Y drivesignal, as shown in FIG. 1B at 30. Eventually, however, the Y drivesignal equals or approximates zero and an essentially horizontal scan 32results. The Y drive signal then reverses polarity and starts toincrease while the X drive signal (essentially an unmodulated squarewave of constant maximum amplitude) remains as before. The minor axis ofthe traces now increases, and the next trace 34 commences.

However, as a consequence the successive ellipses are now traced in ananti-clockwise direction; data is now acquired in the lower (i.e. leftto right) portion of each of these traces so that, throughout the scan,data is acquired left to right, and fly-back (that, with no dataacquisition) is right to left.

Referring to FIG. 1C, eventually a complete, raster-like scan 40 isperformed, after which the Y drive signal (by the end of the scan at itsmaximum amplitude) is switched in polarity to its original polarity andthe process is repeated. The available scan area is of similar shape tothe standard format. The main difference is the increasing curvature forhigh Y values. The central singular point of the prior art spiral scan(cf. FIG. 13) has been avoided, and a nearly square image area isavailable within the 87% spot speed rule.

As mentioned above, the left to right or X drive signal is notmodulated, but is conveniently a constant amplitude square wave that isalso available to gate the Y drive signal. The Y drive signal is basedon a standard raster scanner system signal with slow Y component, butthe standard sawtooth signal is gated by a suitably delayed version ofthe X drive signal to produce the elliptical motion as discussed above.This Y drive signal is shown schematically at 50 in FIG. 2. As will beapparent from this figure, the envelope of this signal has a standardsawtooth form, but the Y drive signal is gated by the fast square wave Xdrive signal to produce the successive elliptical scans withprogressively smaller then larger minor axes. Thus, the initial portion52 corresponds to the clockwise scan portion discussed above byreference, in particular, to FIG. 1A. Eventually the essentiallystraight scan (scan 32 of FIG. 1B) is formed when the Y drive signal 50is essentially zero at point 54. The polarity of the Y drive signal 50is then changed and its magnitude increased through anti-clockwiseportion 56 until a maximum amplitude 58 is reached, after which thewhole sequence recommences. The amplitude of the next trace ismaintained but is of reverse polarity so that a new clockwise scan 60commences.

From the above discussion, it will be apparent that this modulation ofthe minor axis through positive and negative values produces a scan withno discontinuities at the centre of the field, unlike prior artapproaches where the radius of the scan is modulated.

It will also be appreciated that an artifact of modulating the Y drivesignal by means of the X drive signal is that each peak in the Y drivesignal has an oblique rather than flat peak. This means that theelliptical scans will have some distortion, as the minor axis of eachtrace is changing in the course of that trace. This should generally bean insignificant effect, but if preferred, the Y drive signal 50 can bereplaced with a signal in which each maximum is a square wave ofprogressively decreasing or increasing amplitude. Each successiveellipse would therefore be closer to an ideal ellipse. It is notexpected, however, that the approximation represented by the trace ofFIG. 2 would lead to any significant distortion to the ultimate rasterscan or image.

A Y drive signal according to a second preferred embodiment is showngenerally at 70 in FIG. 3. In this embodiment, when a single completescan is being completed (that is, after clockwise traces 72 andanti-clockwise traces 74 [cf. traces 52 and 56 of FIG. 2] have beencompleted), the system does not jump back to the original configurationshown in FIG. 1A. Rather than switching the polarity of the Y drivesignal 70 and commencing a new clockwise scan, the Y drive signal frommaximum 76 onwards is ramped downwards so that another sequence ofanti-clockwise traces 78 is performed. This is done by acquiring dataduring what was previously the fly-back period which, during the lastanti-clockwise trace, resembles the first clockwise trace shown in FIG.1A though in the opposite direction. Thus, by acquiring data during whatwould have been fly-back periods, a sequence of anti-clockwise traces 78is performed and data is acquired. It will be appreciated that as aconsequence successive complete raster scans alternate between left toright data collection (as shown, for example, in FIG. 1C) and right toleft data collection.

In still another (or third) preferred embodiment, the Y scan signal 80(see FIG. 4) is always of one polarity but comprises a first sequence ofclockwise traces 82 with decreasing amplitude followed by a secondsequence of clockwise traces 84 with increasing amplitude. In thisembodiment, the traces proceed essentially as described with respect toFIG. 1A until the essentially horizontal trace is performed after whichthe same sequence of traces is performed in reverse order. Data isacquired during this second set of traces during what was the fly-backperiods of the first set of traces 82. Consequently, the first set oftraces 82 have data acquired from left to right, while the second set oftraces 84 have data acquired from right to left.

It will be appreciated, therefore, that these and other variants can beused according to the present invention to collect a complete set ofdata, according to a user's equipment or other requirements. Indeed, insome embodiments it may be acceptable or desirable that the raster scancomprise essentially the upper half of the complete scan shown in FIG.1C or, indeed, some other portion thereof. It will be appreciated thatthe number of individual traces within any particular raster scan can bedetermined according to requirements and that the above embodiments arepurely illustrative in this respect.

FIG. 5 is a schematic circuit diagram of a scanning apparatus accordingto a fourth preferred embodiment of the present invention, forperforming the various scanning methods of the above describedembodiment.

The apparatus includes a light transmission means in the form of opticalfibre 90 that can be deflected in both X and Y directions as asymmetrical cantilever. It is the tip of this optical fibre 90 that, inresonant operation, describes the elliptical pattern detailed above. Theoptical fibre 90 delivers light from a suitable source (such as a laseror light emitting diode) downstream of the optical fibre 90 but omittedfrom this figure for the sake of clarity. The scanning apparatusincluding optical fibre 90 may form a portion of an endoscope,microscope or endomicroscope.

A forward portion of optical fibre 90 is located adjacent an X drivingcoil 92 and a Y driving coil 94, these coils arranged mutuallyperpendicularly. The optical fibre 90 is provided either with a magnetattached to the fibre adjacent to and acted on by the coils 92, 94 or,alternatively, by coating the optical fibre 90 with a magnetic material(including, for example, certain paints), so that the forces produced bythese coils 92 and 94 can drive the optical fibre 90.

Located toward the rearward end 96 of the movable portion of opticalfibre 90 is a piezoelectric X sensor 98 for producing a voltageaccording to the deflection of the optical fibre 90. The output of Xsensor 98 is ultimately applied to the X driving coil 92, but is firstphase adjusted by phase shifter 100 and amplified by signal processingamplifier 102. If the loop gain is sufficient and the phase correctlyadjusted by phase adjuster 100, the resulting oscillation causes the tipof optical fibre 90 of the cantilever to vibrate in the X direction. Theadjustable phase shifter 100 is included so that the frequency ofoscillation can be suitably positioned on the mechanical resonancecurve, and to compensate for any phase shift in the X sensor 98.

The amplifier 102 also performs some signal processing so that itsoutput is a square wave of adjustable amplitude. This allows directcontrol of the vibration amplitude, and the square wave is also usefulin the generation of the Y drive signal (see FIGS. 2 to 4) for the Ydriving coil 94.

The Y drive signal has a phase that is appropriate to obtain theelliptical motion described above. This is achieved with an adjustabledelay 104 of the square wave used for driving the X driving coil 92. Therequired sweeping amplitude is obtained by using this signal to switch astandard Y sawtooth signal 106, as described above and illustrated inFIGS. 2 to 4. This signal is then applied to the Y driving coil 94. Thecircuit also includes a switch 108 for switching the Y drive signal onor off.

FIG. 6 is an end view (that is, viewed from right to left in FIG. 5) ofthe tip of optical fibre 90 and the X and Y driving coils 92 and 94. Inthis figure can also be seen the core 110 of optical fibre 90, as wellas the magnet 112 attached to the optical fibre 90 so that the X and Ydriving coils 92, 94 can drive optical fibre 90. The use of a magnetallows small adjustments to be made to the position of the magnet 112 onfibre 90 and thereby to the resonance condition of the fibre 90. Owingto the greater mass of magnet 112 (when compared with other embodimentssuch as a painted metallic coating), the driving coils 92, 94 can berelatively small, though at the expense of having a larger and moremassive fibre/magnet combination.

FIG. 7 is a schematic diagram of a scanning apparatus 120, includingassociated electronics 122, according to a fifth preferred embodiment ofthe present invention, for performing the various scanning methods ofthe above described embodiments.

In this embodiment, the scanning apparatus 120 (seen end-on in thisview) includes a scanning mechanism 124 provided with two X solenoids orcoils 126 a,b and two Y solenoids or coils 128 a,b, a light transmittingmeans in the form of optical fibre 130, and axially magnetised permanentmagnet 132. The coils 126 a,b and 128 a,b are located symmetricallyabout fibre 130, while magnet 132 is mounted as a collar on fibre 130and held in place by means of glue. The precise location of magnet 132is discussed in greater detail below by reference to FIG. 9A.

The two X coils 126 a,b are respectively an X drive coil 126 a and aninductive X sensing coil 126 b. The two Y coils 128 a,b are both drivecoils.

In broad terms, the two Y drive coils 128 a,b are connected in seriesand driven such that: (a) force is applied to the magnet 132 and henceto fibre 130 either simultaneously upwards or downwards (in the view ofFIG. 7), and (b) the signals thereby induced into the X sensing coil 126b cancel.

For small deflections, the forces from the two Y coils 128 a,b cancel inthe X direction. With one Y coil (as in the embodiment of FIG. 5), thedesired modulation of the elliptical scanning pattern can be obtained,but with greater difficulty owing to a significant resolved forcecomponent in the X direction during parts of the X scan. Thus, the twodiametrically opposed Y coils 128 a,b provide both electrical andmechanical balance with respect to the X scan.

The drive for the Y coils 128 a,b is generated by switching between apositive and a negative version of the standard Y sawtooth. Thissawtooth Y signal 134 (shown in FIG. 8A) is provided by the imaginingelectronics 136; a signal inverter 138 provides the negative version −Yof that signal. As is discussed in greater detail below, a switch 140 isused to switch between Y and −Y.

As the Y coils 128 a,b are driven upwards and downwards, therebyproviding the Y scan, X sensing coil 126 b outputs an X sensing signal142 (essentially sinusoidal in appearance, as shown in FIG. 8B) that isa function of the position of the magnet 132 (and hence fibre 130). Xsensing signal 142 is phase adjusted by phase adjuster 144 (to providean elliptical scan) and then into amplifier 146. The output of amplifier146 is the X drive input signal 148 (shown schematically in FIG. 8C) ofX drive coil 126 a. The output of amplifier 146 has a maximum voltage,so the resulting oscillating feedback loop 150 (including X sensing coil126 b, phase adjuster 144 and amplifier 146) is ultimately limited toproviding an input signal 148 to X drive coil 126 a that cannot exceedthat maximum. This feedback loop 150 has sufficient gain to oscillateonly when mechanical resonance occurs; hence, the loop runs at afrequency determined by the mechanics of the scanning mechanism 124 andthe electronic phasing.

The input signal 148 to the X drive coil 126 a can then be used togenerate the necessary image synchronising for the fast or X scan. Theimaging electronics in turn can generate the slow Y can or sweep at arate determined by the number of lines required in the image, orequivalently the image rate per second.

As mentioned above, the Y drive signal is obtained by switching betweena positive and a negative version of the standard Y sawtooth signal 134shown in FIG. 8A. This switching is performed by switch 140, which iscontrolled by a signal generated by delaying the X drive input signal148. X drive input signal 148 is fed into delay 154, which outputs theswitch control signal 156 (depicted in FIG. 8D) suitably phase adjustedso that the elliptical scan path of the tip of fibre 130 has astationary major axis. This switch control signal 156 then controlsswitch 140 to alternative been sawtooth Y signal 134 and −Y at the rateof the X drive input signal, and the resulting output signal from switch140 is the ultimate Y drive input signal 158 applied to the Y coils 128a,b. This Y drive input signal 158 is shown in FIG. 8E.

As the switch 140 is ultimately controlled by the X drive input signal148 (through delay 154), the X sensor comprising X sensing coil 126 bprovides both X and Y feedback. Consequently, a Y sensor is not neededin this embodiment.

The X input drive signal 148 is also used as a X synchronisation signal,and fed into the imaging electronics 136. The imaging electronics 136generates the sawtooth Y signal 134 at a rate determined by the numberof lines required in the image, or equivalently the image rate persecond.

Referring to FIG. 8A, sawtooth signal 134 has two components: the traceregion 160 of positive gradient and a steeper retrace region 162 ofnegative gradient 162. The former corresponds to the trace portion of asingle complete scan (i.e. when image data are collected); the latterportion corresponds to the retrace portion of the scan when data isgenerally not collected, and can hence be of shorter duration. Inprinciple the retrace portion should be completed as quickly as possible(cf. FIG. 2), but this retracing is not performed too quickly in thisembodiment lest the fibre 130 “bounce” upon return its return to theposition corresponding to the scan starting position.

Referring to FIG. 8E, these trace and retrace regions have correspondingregions in the Y drive input signal 158 as shown in FIG. 8E; the pointof the Y drive input signal 158 corresponding to the centre of the scanis also indicated at 164.

The envelope 166 of the resulting scan of the fibre 130 within the spacedefined by the X and Y coils 126 a,b and 128 a,b is indicated in FIG. 7;it will be understood that the tip of fibre 130, as it extends beyondthe drive coils, will generally have larger envelope of motion thanenvelope 166.

It will also be appreciated by those in the art that, because X coils126 a,b and Y coils 128 a,b are identical, it is a straightforwardmatter to swap X and Y axes. Electronics 122 can be modified by theaddition of a suitable switch and minor duplication of some of itscircuitry so that the coils 126 a,b act as Y drive coils and coils 128a,b act—respectively—as an X drive coil and an X sensing coil. Theapparatus 120 then functions as described above, except that the X and Ydirections are swapped. In prior art systems, scans in perpendiculardirections can only be obtained by manually rotating the scanningapparatus. In hand-held devices, the operator manually twists thehand-piece, requiring in some cases substantial dexterity and generallywith considerable imprecision. The symmetry of the scanning mechanism124 of FIG. 7 allows such an operation to be performed without eitherimpediment.

It should also be noted that the basic scanning mechanism of FIG. 7could be used to provide other scan patterns, if operated with suitableelectronics. It need not be operated resonantly and it need not belimited to elliptical scan envelopes. For example, resonant andnon-resonant scan patterns could be generated, including (in addition tothe aforementioned elliptical—including circular—scan patterns) spiralpatterns and figure eight scan patterns.

FIG. 9A is a partial cross-sectional view of an endoscope head 168provided with scanning mechanism 124 inside the endoscope head casing170 (of internal diameter 4.45 mm and external diameter 4.71 mm), inwhich are visible the relative positions of the Y drive coils 128 a,b,fibre 130 and magnet 132. It will be seen that the tip 172 of the fibre130 executes a path of greater size that the portion 174 of the fibre130 located between the Y drive coils 128 a,b.

Each of the X and Y coils 126 a,b and 128 a,b has a diameter of 1.45 mmwith a core diameter of 0.60 mm.

The length of the vibrating portion of the fibre 130 is 12.5 mm; thefibre's diameter is 0.125 ml. The magnet 132 has a length of 2 mm anddiameter of 0.48 mm. The distance from the base of the fibre 130 to themagnet 132 is 2 mm. The resonant frequency of the fibre 130 plus magnet132 assembly can be set so as not to differ greatly from that of thefibre 130 alone, by adjustment of its location on the fibre 130. Thefibre 130 is fixed at its base 174 centrally in an end plate 176 of theendoscope head 168; the end plate 176—and hence the length of the base174 of the fibre 130 anchoured in the end plate 176—is 3 mm.

The end plate 176 acts as an anchour for base 174 of fibre 130; itsecures the fibre but can also influence the vibration of the fibre. Forthis reason, it may be desirable to provide an optional collar aroundthe fibre 130 abutting and forward (i.e. to the right in this figure) ofthe end plate 176. This collar could either have a simple circularaperture in which the fibre 130 is secured. Referring to the end view ofFIG. 9B, such a collar 177 could instead be provided with a cut-out orslot 178 aligned in the X direction so that the collar 177 in factcomprises two D-shaped portions 179 a,b clamping the fibre 130therebetween. The cut-out or slot 177 would then encourage vibration inthe X direction (i.e. that of the fast scan), thereby reducing bias witha component in the Y direction.

The X and Y coils 126 a,b and 128 a,b each have a diameter of 1.3 mm andlength of 2 mm.

In tests of this embodiment performed by the inventors, resonance at anX drive input signal frequency (cf. FIG. 8C) of 611 Hz was achieved;this also implies the same frequency for the high frequency component ofthe Y drive input signal 158 (cf. FIG. 8E). Peak-to-peak fibre tipdeflection was 4.0 mm. The resonant frequency of the mechanism 124 butwithout magnet 132 was found to be 642 Hz.

Generally speaking, resonant frequency increases as the size of thescanning mechanism 124 is reduced. Calculations suggest that—even withthe version shown in FIG. 9A—higher frequencies could be obtained (ifdesired) by providing attachment between the fibre 130 and magnet 132over the entire length of the magnet. Higher resonant frequencies couldalso be obtained by increasing the effective diameter and hence mass offibre 130 by adding a “collar” or a “capillary” around it in the regionimmediately forward of its base 174 or underneath the magnet 132. Forexample, these portions of fibre 130 could be increased in effectivediameter to ˜0.250 mm. Furthermore, higher resonant frequencies could beobtained by tapering the fibre 130 towards its tip 172. Furthermodifications of the resonant frequency can also be effected byadjusting other mechanical properties of the mechanisms (such as thelength or mass of the magnet).

Further, in the above discussion references to resonant frequency referto the fundamental resonance frequency. Nevertheless, the scanningmechanism of the various embodiments could also be operated in first andsecond harmonic frequency modes (as have been tested by the presentinventors) and, by straightforward adjustment, in higher order modes. Ineach case, the mechanism remains resonant and hence stores mechanicalenergy leading to reduced jitter and greater stability.

Referring to FIG. 9C, in an alternative configuration of thisembodiment, magnet 132 is located forward of the coils, so that the Xand Y coils 126 a,b and 128 a,b are not required to accommodate themagnet 132. Consequently, Y drive coils 128 a,b can be located moreclosely to each other (as, though not shown, are X drive coils 126 a,b)and the overall diameter of the casing 170 can be reduced. Thisconfiguration permits the provision of an endoscope head of reduceddiameter.

Various tests have also been performed to ascertain the characteristicsof scanning mechanism 124. FIG. 10A depicts plots of resonant frequencyf(Hz) against fibre length l(mm), without a magnet (solid curve 180),with a magnet of 2 mm length and 0.40 mm diameter (dotted curve 182),and with a magnet of 2 mm length and 0.48 mm diameter (dashed curve184). In each case the length of the base of the fibre was 2 mm and thefibre had a diameter of 0.125 mm.

FIG. 10B depicts plots of radius of the tip movement R(mm) against fibrelength l(mm) for a magnet of 2 mm length and 0.48 mm diameter (solidcurve 186) and 0.40 mm diameter (dotted curve 188). (The region 190bounded by horizontal dotted lines R=9 mm and R=10 mm represents therange of tip movement obtained with certain prior art scanningmechanisms that employ a tuning fork to provide the fast or X scan.)

FIG. 10C depicts plots of mechanical magnification m (calculated as theratio of fibre tip deflection to magnet deflection) against fibre lengthl(mm), for a magnet of 2 mm length and 0.48 mm diameter (solid curve190) and 0.40 mm diameter (dotted curve 192).

FIG. 11 depicts the results of a theoretical comparison of scan areasthat could be obtained for raster patterns obtained with a prior arttuning-fork type scanning mechanism and with an apparatus comparable tothat of FIG. 7, in order to compare the scan areas available to theoptics of, for example, an endoscope. The scan areas were defined by thescan speed criterion, set by the 2:1 rule in the sine-linear model (thatis, the square area of half the peak to peak X mechanical deflection,and the peak to peak Y deflection). This is referred to above as the“87% rule”, in which image data are not gathered when scanning speeddrops below 87% of peak speed.

In FIG. 11, it can be seen that the endoscope head 200 (set to aninternal diameter of 2.75 mm) delimits the motion of both the prior arttuning fork tine 202 (on which is mounted optical fibre tip 204) and theelliptically scanned optical fibre tip 206 of an embodiment of thepresent invention. It will be noted that tine 202 is depicted in fivepositions, including a central (at rest) position and four extremes ofits motion. The upper and lower right extremes of motion of tine 202 (asseen in this figure) are fixed by the endoscope head 200; for asymmetrical scan of the fibre tip 204, the left excursion has someclearance compared with the right so the upper and lower left extremesof motion of tine 202 are somewhat within the confines of endoscope head200.

The result for the tine 202 of the prior art tuning fork scanningmechanism is a familiar 2:1 square-in-rectangle diagram, that is, themechanics of this arrangement define a rectangular scan (defined by theextreme positions of the fibre tip 204) and, owing to the 87% speedrule, the optics define a square, usable scan area (indicated by dashedsquare 208) within that rectangle. The peak-to-peak X deflection of thetine 202 was 2.0 mm, the peak-to-peak Y deflection 1.0 mm. The imagearea (i.e. of square 208) for this arrangement was thus 1.00 mm².

The fibre tip 206 of the embodiment of the present invention alsotouches the endoscope head 200, which thus delimits its maximum motion.The peak-to-peak deflection of the fibre tip 206 can be essentially theentire internal diameter of the endoscope head (or more exactly theendoscope head internal diameter minus the fibre external diameter); asno tine is involved, the modulated elliptical scan can therefore covermore area that the prior art arrangement. Usable imaging area is alsogreater: scanning speed above 87% of peak speed is denoted by solidcurves 210, while lower speeds are shown by means of dotted curves 212.

It will be seen that the scan area of the modulated elliptical scan isgreater than that of the fibre tip 204 mounted on tine 202. This is duein part to the more compact size of a fibre alone (compared with theprior art fibre/tine combination), but also to the higher strain thatthe silica of the fibre of the inventive embodiment can withstandrelative to the steel of the prior art tine, even at the same frequency.

Modifications within the scope of the invention may be readily effectedby those skilled in the art. For example, while, according to thepresent invention, eccentricity or minor axis are adjusted to achievethe scanning pattern, in some embodiments it may be desirable also tomodulate the radius during operation. It is to be understood, therefore,that this invention is not limited to the particular embodimentsdescribed by way of example herein above.

In the claims that follow and in the preceding description of theinvention, except where the context requires otherwise owing to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but not to preclude thepresence or addition of further features in various embodiments of theinvention.

Further, any reference herein to prior art is not intended to imply thatsuch prior art forms or formed a part of the common general knowledge.

1. A method of scanning a light transmitter having an exit tip,comprising moving said tip in an elliptical pattern while varying theeccentricity of said elliptical pattern.
 2. A method as claimed in claim1, including varying said eccentricity by varying the length of one axisof said elliptical pattern.
 3. A method as claimed in claim 2, includingvarying said eccentricity by varying the length of the minor axis ofsaid elliptical pattern.
 4. A method as claimed in claim 1, wherein saidelliptical pattern has a major axis and minor axis in the ratio ofapproximately two.
 5. A method as claimed in claim 1, wherein said lighttransmitter is an optical fiber.
 6. A method as claimed in claim 1,including driving said light transmitter magnetically.
 7. A method asclaimed in claim 6, including driving said light transmitter with amagnet attached to said light transmitter, wherein said magnet ismagnetised axially and acted on by mutually perpendicular coils orwindings.
 8. A scanning apparatus, comprising: a light transmitterhaving an exit tip; first and second drives for resonantly driving saidlight transmitter in orthogonal directions; wherein said first andsecond drives are operable to move said tip in an elliptical patternwhile varying the eccentricity of said elliptical pattern.
 9. Anapparatus as claimed in claim 8, wherein said apparatus is operable tovary said eccentricity by varying the length of one axis of saidelliptical pattern.
 10. An apparatus as claimed in claim 8, wherein saidapparatus is operable to vary said eccentricity by varying the length ofthe minor axis of said elliptical pattern.
 11. An apparatus as claimedin claim 8, wherein said first and second drives are in the form of amagnetic drive for driving said light transmitter.
 12. An apparatus asclaimed in claim 11, wherein said magnetic drive (i) a magnet attachedto said light transmitter and (ii) mutually perpendicular coils orwindings, wherein said magnet is magnetised axially and acted on by saidmutually perpendicular coils or windings.
 13. An optical fiberendoscope, microscope or endomicroscope including a scanning apparatusas claimed in claim
 8. 14. An optical fiber confocal endoscope,microscope or endomicroscope including a scanning apparatus as claimedin claim
 8. 15. A scanning apparatus comprising: an X drive for drivinga light transmitter having an exit tip in an X direction; a Y drive fordriving said light transmitter in a Y direction; an X drive input signalgenerator for providing an X drive input signal; and a Y drive inputsignal generator for providing a Y drive input signal modulated by amodulating signal derived from said X drive input signal; wherein saidapparatus is operable to scan said exit tip in an elliptical scanpattern with varying eccentricity when said exit tip is drivensimultaneously by said X drive and said Y drive.
 16. A scanningapparatus as claimed in claim 15, wherein: said X drive input signalcomprises a square wave signal; and said Y drive input signal generatoris configured to provide a sawtooth signal modulated by said modulatingsignal.
 17. An apparatus as claimed in claim 16, wherein said Y driveinput signal generator is operable to generate said sawtooth signal suchthat said sawtooth signal is repeatedly inverted according to a triggersignal comprising a delayed version of said X drive input signal.
 18. Anapparatus as claimed in claim 17, wherein said apparatus is operable tocollect image data from said central portion of said scan patterncorresponding to an exit tip speed of greater than or equal toapproximately 87% of a peak exit tip speed.
 19. An apparatus as claimedin claim 15, wherein said scan pattern is elliptical and has aneccentricity that is always greater than zero.
 20. An apparatus asclaimed in claim 15, wherein said X drive and said Y drive are in theform of a magnetic drive comprising (i) a magnet attached to said lighttransmitter and (ii) mutually perpendicular coils or windings, whereinsaid magnet is magnetised axially and acted on by said mutuallyperpendicular coils or windings and said mutually perpendicular coils orwindings comprise a pair of drive coils located symmetrically each onopposite sides of a rest position of said magnet in a first plane, and afurther drive coil located in a second plane perpendicular to said firstplane, and said apparatus further comprises a sensing coil for sensingthe position of said magnet and located in said second planesymmetrically opposite said magnet from said further drive coil, whereineach of said pair of coils, said further coil and said sensing coil areequidistant from said magnet in said rest position, said sensing coil isoperable to output an output signal indicative of said position of saidmagnet, and said apparatus is operable to derive an input signal forsaid further coil from said output signal.
 21. An apparatus as claimedin claim 20 wherein said apparatus is operable to control a) said pairof coils in said first plane and b) said further coil and said sensingcoil in said second plane, to swap functions so that said pair of drivecoils in said first plane act as a drive coil and a sensing coil, andsaid further coil and said sensing coil in said second plane act as apair of drive coils, wherein said apparatus can perform a further scanperpendicular to said scan pattern.
 22. An optical fiber endoscope,microscope or endomicroscope including a scanning apparatus as claimedin claim
 15. 23. An optical fiber confocal endoscope, microscope orendomicroscope including a scanning apparatus as claimed in claim 15.24. A method of scanning a light transmitter having an exit tip,comprising moving said tip in an elliptical pattern while varying theeccentricity of said elliptical pattern, and repeatedly varying saideccentricity between a minimum value and one.
 25. A method of scanning alight transmitter having an exit tip, comprising moving said tip in anelliptical pattern while varying the eccentricity of said ellipticalpattern, and repeatedly varying said eccentricity from a minimum valueto one and then back to said minimum value, whereby a portion of saidpattern centered on the center of said elliptical pattern approximates araster pattern.
 26. A method of scanning a light transmitter having anexit tip, comprising moving said tip in an elliptical pattern whilevarying the eccentricity of said elliptical pattern, and modulating saideccentricity by modulating the minor axis of said elliptical patternbetween positive and negative extremes, so that said tip moves in bothclockwise and counterclockwise directions in the course of a singlecomplete scan.
 27. A method of scanning a light transmitter having anexit tip, comprising moving said tip in an elliptical pattern whilevarying the eccentricity of said elliptical pattern, driving said tipwith an X drive parallel to the major axis of said elliptical patternand with a Y drive parallel to the minor axis of said ellipticalpattern, and synchronising at a constant phase to the X scan to allowinterfacing to a standard raster display.
 28. A method as claimed inclaim 27, including deriving said Y drive by synchronously switching adelayed version of said X drive.
 29. A method of scanning a lighttransmitter having an exit tip, comprising: moving said tip in anelliptical pattern while varying the eccentricity of said ellipticalpattern; driving said light transmitter magnetically with a magnetattached to said light transmitter, wherein said magnet is magnetisedaxially and acted on by mutually perpendicular coils or windings thatcomprise a pair of drive coils located symmetrically each on oppositesides of a rest position of said magnet in a first plane, and a furtherdrive coil located in a second plane perpendicular to said first plane;sensing the position of said magnet with a sensing coil located in saidsecond plane symmetrically opposite said magnet from said further drivecoil; obtaining an output signal from said sensing coil indicative ofsaid position of said magnet; and deriving an input signal for saidfurther drive coil from said output signal; wherein each of said pair ofdrive coils, said further drive coil, and said sensing coil areequidistant from said magnet in said rest position.
 30. A method asclaimed in claim 29, further including controlling a) said pair of coilsin said first plane and b) said further coil and said sensing coil insaid second plane, to swap functions so that said pair of drive coils insaid first plane act as a drive coil and a sensing coil, and saidfurther coil and said sensing coil in said second plane act as a pair ofdrive coils, whereby a further scan can be performed perpendicular tosaid elliptical pattern.
 31. A method of scanning a light transmitterhaving an exit tip, comprising moving said tip in an elliptical patternwhile varying the eccentricity of said elliptical pattern, includingdriving said light transmitter magnetically, wherein said lighttransmitter is provided with a coat of magnetic material or locatedwithin a close-fitting magnetic tube.
 32. A scanning apparatus,comprising: a light transmitter having an exit tip; and first and seconddrives for resonantly driving said light transmitter in orthogonaldirections; wherein said first and second drives are operable to movesaid tip in an elliptical pattern while varying the eccentricity of saidelliptical pattern, and said apparatus is operable to repeatedly varysaid eccentricity between a minimum value and one.
 33. A scanningapparatus, comprising: a light transmitter having an exit tip; and firstand second drives for resonantly driving said light transmitter inorthogonal directions; wherein said first and second drives are operableto move said tip in an elliptical pattern while varying the eccentricityof said elliptical pattern, wherein said apparatus is operable torepeatedly vary said eccentricity from a minimum value to one and thenback to said minimum value, and wherein a portion of said patterncentered on the center of said elliptical pattern approximates a rasterpattern.
 34. A scanning apparatus, comprising: a light transmitterhaving an exit tip; first and second drives for resonantly driving saidlight transmitter in orthogonal directions; wherein said first andsecond drives are operable to move said tip in an elliptical patternwhile varying the eccentricity of said elliptical pattern, and whereinsaid apparatus is operable to modulate said eccentricity by modulatingthe minor axis of said elliptical pattern between positive and negativeextremes, so that said tip moves in both clockwise and counterclockwisedirections in the course of a single complete scan.
 35. A scanningapparatus, comprising: a light transmitter having an exit tip; and firstand second drives for resonantly driving said light transmitter inorthogonal directions; wherein said first and second drives are operableto move said tip in an elliptical pattern while varying the eccentricityof said elliptical pattern, wherein said first drive comprising an Xdrive for driving said tip parallel to the major axis of said ellipticalpattern and said second drive comprising a Y drive for driving said tipparallel to the minor axis of said elliptical pattern, and wherein saidapparatus is operable to synchronise at a constant phase to the X scanto allow interfacing to a standard raster display.
 36. An apparatus asclaimed in claim 35, wherein said Y drive is derived by synchronouslyswitching a delayed version of said X drive.
 37. A scanning apparatus,comprising: a light transmitter having an exit tip; and a magnetic drivefor resonantly driving said light transmitter in orthogonal directionsand operable to move said tip in an elliptical pattern while varying theeccentricity of said elliptical pattern, said magnetic drive comprising(i) a magnet attached to said light transmitter and (ii) mutuallyperpendicular coils or windings, said magnet being magnetised axiallyand acted on by said mutually perpendicular coils or windings; whereinsaid mutually perpendicular coils or windings comprise a pair of drivecoils located symmetrically each on opposite sides of a rest position ofsaid magnet in a first plane, and a further drive coil located in asecond plane perpendicular to said first plane, and wherein saidapparatus further comprises a sensing coil for sensing the position ofsaid magnet and located in said second plane symmetrically opposite saidmagnet from said further drive coil, wherein each of said pair of coils,said further coil and said sensing coil are equidistant from said magnetin said rest position, said sensing coil is operable to output an outputsignal indicative of said position of said magnet, and wherein saidapparatus is operable to derive an input signal for said further coilfrom said output signal.
 38. An apparatus as claimed in claim 37,wherein said apparatus is operable to control a) said pair of coils insaid first plane and b) said further coil and said sensing coil in saidsecond plane, to swap functions so that said pair of drive coils in saidfirst plane act as a drive coil and a sensing coil, and said furthercoil and said sensing coil in said second plane act as a pair of drivecoils, wherein said apparatus can perform a further scan perpendicularto said elliptical pattern.
 39. A scanning apparatus, comprising: alight transmitter having an exit tip; and a magnetic drive forresonantly driving said light transmitter in orthogonal directions andoperable to move said tip in an elliptical pattern while varying theeccentricity of said elliptical pattern; wherein said light transmitteris provided with a coat of magnetic material or is located within aclose-fitting magnetic tube.
 40. A scanning apparatus comprising: an Xdrive for driving a light transmitter having an exit tip in an Xdirection; a Y drive for driving said light transmitter in a Ydirection; an X drive input signal generator for providing an X driveinput signal; and a Y drive input signal generator for providing a Ydrive input signal modulated by a modulating signal derived from said Xdrive input signal; wherein said exit tip executes a scan pattern whendriven simultaneously by said X drive and said Y drive, said X driveinput signal comprises a square wave signal, and said Y drive inputsignal generator is configured to provide a sawtooth signal modulated bysaid modulating signal.
 41. An apparatus as claimed in claim 40, whereinsaid Y drive input signal generator is operable to generate saidsawtooth signal such that said sawtooth signal is repeatedly invertedaccording to a trigger signal comprising a delayed version of said Xdrive input signal.
 42. An apparatus as claimed in claim 41, whereinsaid apparatus is operable to collect image data from said centralportion of said scan pattern corresponding to an exit tip speed ofgreater than or equal to approximately 87% of a peak exit tip speed. 43.An optical fiber endoscope, microscope or endomicroscope including ascanning apparatus as claimed in claim
 40. 44. A scanning apparatuscomprising: a magnetic drive comprising an X drive for driving a lighttransmitter having an exit tip in an X direction and a Y drive fordriving said light transmitter in a Y direction; an X drive input signalgenerator for providing an X drive input signal; and a Y drive inputsignal generator for providing a Y drive input signal modulated by amodulating signal derived from said X drive input signal; wherein saidexit tip executes a scan pattern when driven simultaneously by said Xdrive and said Y drive, wherein said magnetic drive comprises (i) amagnet attached to said light transmitter and (ii) mutuallyperpendicular coils or windings, wherein said magnet is magnetisedaxially and acted on by said mutually perpendicular coils or windingsand said mutually perpendicular coils or windings comprise a pair ofdrive coils located symmetrically each on opposite sides of a restposition of said magnet in a first plane, and a further drive coillocated in a second plane perpendicular to said first plane, whereinsaid apparatus further comprises a sensing coil for sensing the positionof said magnet and located in said second plane symmetrically oppositesaid magnet from said further drive coil, and wherein each of said pairof coils, said further coil and said sensing coil are equidistant fromsaid magnet in said rest position, said sensing coil is operable tooutput an output signal indicative of said position of said magnet, andsaid apparatus is operable to derive an input signal for said furthercoil from said output signal.
 45. An apparatus as claimed in claim 44,wherein said apparatus is operable to control a) said pair of coils insaid first plane and b) said further coil and said sensing coil in saidsecond plane, to swap functions so that said pair of drive coils in saidfirst plane act as a drive coil and a sensing coil, and said furthercoil and said sensing coil in said second plane act as a pair of drivecoils, wherein said apparatus can perform a further scan perpendicularto said scan pattern.
 46. An optical fiber endoscope, microscope orendomicroscope including a scanning apparatus as claimed in claim 44.